Chemically resistant silver alloy



Patented June 2, @352 PETER. ASSMANBT, 61" LUDWIGSHAFIEN-GN-THE-RHHJE, GERMANY, ASS-EGNQR T0 1. G. FEEBEEIINDUSTRIE AKTIENG'ESELLSGHAFT, 0F riaAnnron'r-ou-rnnnsam, one

mail 1.

GHIEEEGALLY EESISTAN'E SILVER ALLOY No Brewing. Application filed December e, 19:29, Serial Ito. 4.11.684, and in Germany June it, W26

The present invention relates to cally resistant silver alloy.

The present application is a continuation in part of the application for an improvement 5 in chemically resistant alloys Ser. No.

199,403, filed June 16, 1927.

The employment of silver as a material for receptacles and apparatus, which come into contact with chemicals, especially hydrochloric acid, is well known. Alloys of silver containing preferably from 20 to per cent of copper are mostly employed for the production of silverware for general use. Such alloys are more suitable than pure silver with regard to their mechanical properties, but they have the great disadvantage of being less resistant to corrosion than pure silver.

I have now found that silver alloys, which consist of at least 78 per cent of silver and between 0.3 and about 20 percent of aluminium, and between 0.3 and 18 per cent of at least one metal selected from the group ofmetals belonging to from the second to the fifth a chemigroup of the periodic system and capable of 25 forming solid solutions rich in silver are considerably better than. pure silver or the silver alloys hitherto marketed, for example as regards their resistance to corrosion. The said group of metals capable of forming solid solutions rich in silver, comprise for example magnesium, zinc, tin, thallium, antimony, arsenic, bismuth and silicon. The durability of the said alloys is particularly excellent against the action of aqueous hydrochloric acid of any concentration. For example all the alloys with a content or" from 5 to 20 per cent of aluminium are completely resistant to the action of dilute hydrochloric acid.

Alloys of the kind described particularly noticeable by their resistivity against chemical corrosion are those containing up to about 15 per cent of thallium besides aluminium. A suitable alloy is, for instance, one containing 80 per cent of silver, 10 per cent of thal- .e lium and 10 per cent of aluminium. The

chemical resistance is not only impaired by the addition of aluminium, but, in some cases, for instance against the action chloric acid of any concentration, even enhanced. It is advisable, in the production of hydrob of cast were from silver-aluminium-thallium alloys to allow the cast to cool very slowly, or to heat the finished article to about 400 C. for several hours, by means of which a completely homogeneous alloy is obtained. As further suitable compositions of silver-aluminium-thallium alloys there may be mentioned alloys consisting of at least '28 per cent of silver, from 0.3 to 8 per cent of aluminium, from 0.5 to 20 per cent of thallium to which may be added from 0.3 to 20 per cent of zinc and tin, either single or in any desired proportion.

As an example of an alloy suitable for east ing the following composition may be men- 6 tioned: 81.0 per cent of silver, 8.? per cent of aluminium, on per cent of antimony, and 3 per cent of tin: Tests, in which the said alloy was placed for 4 weeks in pure concentrated hydrochloric acid, showed that the durability of this alloyreekoned on the weight of the alloy-was five times better than that of pure silver. All these alloys are highly resistant to chemical reagents, especially to hydrochloric acid, acid food-studs, perspiration, hydrogen sulphide and the like, and are therefore most excellently adapted as materials for the production of receptacles and apparatus coming into contact with chemical reagents, especially hydrochloric acid, and of silver-Ware for general use. p

The alloys containing thallium are particularly suitable for the latter purpose, in the first place, since the blackening of silverware, which is so disagreeable in general use, is completely prevented by the presence of thallium, and secondly as regards lustre and colour, as such alloys can hardly be distinguished from pure silver, so that they are far superior in this respect to any of the silver alloys hitherto in trade. Tli, said alloys may be produced either frolnf' pure silver or from such containing considerable amounts of impurities. It is therefore not necessary to employ pure silver for the preparation of the alloys according to my invention, the usual silver-copper alloys may e used as well but only in such amounts that the final alloy contains at the most 6' per cent of copper.

It is of course immaterial in most cases with regard to the chemical resistance, Whether the articles or apparatus are made throughout of the said silver alloys, or Whether only the surfaces exposed to the attack are provided with a lining or coating of the alloys.

What I claim is 1. A silver alloy consisting of at least 78 per cent of silver, from 0.3 to 20 per cent of aluminium and from 0.3 to 18 per cent of at least one metal selected from the group consistingx of thallium, zinc and tin.

2. silver alloy consisting of at least 78 per cent of silver, from 0.3 to 8 per cent of aluminium and from 0.5 to 18 per cent of thallium.

3. A silver alloy consisting of at least 78 per cent of silver, from 0.3 to 8 per cent of aluminium, from 0.5 to 17.7 per cent of thallium and from 0.3 to 17.5 per cent of zinc.

4. A silver alloy consisting of at least 7 8 per cent of silver, from 0.3 to 8 per cent of aluminium, from 0.5 to 17.7 per cent of thallium and from 0.3 to 17.5 per cent of a mixture of zinc and tin in any proportion.

In testimony whereof I have hereunto set my hand.

PETER ASSMANN. 

